OP
Octopus
To save me wading through all the posts, for clarity when you say 30ma RCD do you mean 1 RCD or multiple RCD's?
Discuss Very Hi ZS Reading on TT system? any advice in the Australia area at ElectriciansForums.net
To save me wading through all the posts, for clarity when you say 30ma RCD do you mean 1 RCD or multiple RCD's?
I refuse to get involved!! lol!!!
yeah well this one cropped up here a while back......2 RCDs..both 30mA...both in series...one feeds the house..the other the garage/outbuilding...theres a fault in the garage/outbuilding...which lets go first?...It wouldn't "slow the discrimination time? " but it would mean there was no discrimination between the RCD's and it would be pot luck which would trip first. inconvenient at best, dangerous at its worst. First one should be time delayed or S type
i got confused earlier, because a member said the my ZS reading could never be lower than my ZE...
My ZS of 2.6 etc is lower than 187 omhs.....?
It's often lower because of parallel paths from bonding conductors etc. I explained in post 4.
Your 187 Ohms is Ra NOT Ze on a TT system, this is all in the On-Site Guide that you already mentioned, PLEASE read it thoroughly, there are large gaps in your knowledge and someone could be hurt because of this!
You're scaring me Eng54. :aureola: This isn't some kinda new years resolution is it?
how about a lovely gas pipe..lol....Not really, just that there are more than enough posters on this thread already!! lol!!
Does seem strange though, that the OP is more than satisfied with his Ra of 185 ohms or whatever, ...and for his own house!! Seems he didn't even give a thought to adding a couple of rods at the workshop end, or adding on a rod, at the existing rod for the house.... Oh well, his house and his family!!! lol!!!
Not really, just that there are more than enough posters on this thread already!! lol!!
Does seem strange though, that the OP is more than satisfied with his Ra of 185 ohms or whatever, ...and for his own house!! Seems he didn't even give a thought to adding a couple of rods at the workshop end, or adding on a rod, at the existing rod for the house.... Oh well, his house and his family!!! lol!!!
how about a lovely gas pipe..lol....
just to confirm, I never said I was satified with my high RA, just giving the facts and hope to get good information from the forum.
I will be looking to lower the RA, however it is deemed as ok according to the Regs..
how about a lovely gas pipe..lol....
spend effort getting it as low as you can.....much lower than this magic 200 ohms....can be done...deep rod/s.....The Reg's are badly written on this point, it leaves newly trained and inexperienced electricians with the idea that 200 ohms is the figure to comply with, ie the max Ra. It doesn't mean that at all.... They are only referring to stability, which i find is wishful thinking, at anywhere near 200 ohms with a 1.2m rod. You need ''Depth'' to achieve that!!!
spend effort getting it as low as you can.....much lower than this magic 200 ohms....can be done...deep rod/s.....
542.2.4.....I may be completely wrong (forgive me!) but I thought it was ok to use pipework as a ground rod, as long as the owner was aware that it was being used as such (so knew not to remove/replace it without giving thought to it's electrical function)
Is this true, or complete nonsense that I've picked up somewhere? I guess in most cases the water/gas pipes are owned by the suppliers anyway, not the property owner, so this wouldn't be applicable.
542.2.4.....
no probs matey...the amount of stuff i have got totally wrong in here..lol......I'm glad I didn't completely imagine that, even if I got it half wrong!
I may be completely wrong (forgive me!) but I thought it was ok to use pipework as a ground rod, as long as the owner was aware that it was being used as such (so knew not to remove/replace it without giving thought to it's electrical function)
Is this true, or complete nonsense that I've picked up somewhere? I guess in most cases the water/gas pipes are owned by the suppliers anyway, not the property owner, so this wouldn't be applicable.
The Reg's are badly written on this point, it leaves newly trained and inexperienced electricians with the idea that 200 ohms is the figure to comply with, ie the max Ra. It doesn't mean that at all.... They are only referring to stability, which i find is wishful thinking, at anywhere near 200 ohms with a 1.2m rod. You need ''Depth'' to achieve that!!!
To the OP.....ignore this.
There is nothing wrong with the UK max Ra of 200 ohms, as long as your system is protected by RCD's,preferably an up front 100ma S type at the origin,and 30ma protection to final circuits...a single rod with an Ra of 187 ohms is perfectly adequate and acceptable.
Unless you achieve a sub 2 ohm Ra you are wasting your time attempting to improve it...ie,if you drive in more rods and achieve 10 ohms,an Ra most would consider very low,your PEFC will be 23a...not a lot of use for most OCPD's,you are still reliant on the RCD for earth fault protection so you may as well have left it at 187 ohms.
As already stated,your Zs readings are low..(not high)...due to parallel paths through bonding etc and are acceptable.
unfortunately i`m still on the red book markie which has it as 542.2.4...as i quoted......will be getting the green one shortly.....It used to be acceptable (<=15th edition) to use private water supply pipework as an earth electrode. "Old hands" have probably mentioned it in the past and maybe this is what you have a vague memory of.
Now of course the practice is is prohibited by 542.2.6
unfortunately i`m still on the red book markie which has it as 542.2.4...as i quoted......will be getting the green one shortly.....
its sorted and will be in the post shortly...courtesy of Widdler...£55 including postage for the BGB and the osg...not bad eh?....Get someone who is a member of the IET to get it for you as its £52 for IET members pls the onsite is £15
its sorted and will be in the post shortly...courtesy of Widdler...£55 including postage for the BGB and the osg...not bad eh?....
To the OP.....ignore this.
There is nothing wrong with the UK max Ra of 200 ohms, as long as your system is protected by RCD's,preferably an up front 100ma S type at the origin,and 30ma protection to final circuits...a single rod with an Ra of 187 ohms is perfectly adequate and acceptable.
Unless you achieve a sub 2 ohm Ra you are wasting your time attempting to improve it...ie,if you drive in more rods and achieve 10 ohms,an Ra most would consider very low,your PEFC will be 23a...not a lot of use for most OCPD's,you are still reliant on the RCD for earth fault protection so you may as well have left it at 187 ohms.
As already stated,your Zs readings are low..(not high)...due to parallel paths through bonding etc and are acceptable.
Absolutely agreed, what is this weird obsession with trying to obtain TN values on a TT system?
Someone will post a reply regarding unreliable RCDs, I'll ask for just 1 example of a death or injury from this scenario, none can be found!
The reg's, BS 7430 (earthing) and Guidance Note 8 are perfectly clear and logical regarding TT Ra values.
I had one the other day on an EICR...RCD let go alright ..on test that is....but came to the manual (push button) test at the end of the 6.....wouldn`t let go......an instant condemnment.....And the above is basically why, the UK has crap TT systems and always will do, with the perpetuation of some of the stupid comments such as these two examples...
200 ohms from a 1m rod is about as useful as using a bent screwdriver to tighten a screw, be it for the Ra or it's stability! The UK's obsession with this crazy figure of 200ohms (which is based only on stability) is about as far from logical as you can get. No other country that i know of, has or mentions such a high limit, of anywhere approaching that figure. Yet both of you are trying to defend it!! It is indefensible and that section of the Reg's is in dire need of a revision. ...In fact there was talk of a lowered figure being pushed for inclusion into the last batch of amendments...
No-ones trying to obtain disconnection times equal to a TN system, but that's not by any means an impossibility either. But the lower an Ra is, the better the chances of having a protective device trip in a relatively decent enough time, not to cause fire or maybe possible injury, despite a non-functioning cure-all RCD... Great if you have parallel earths from water/gas bonding to help you along, well until they come along and replace with plastic that is...
And yes your quite right, RCD's DO fail and a lot more often than either of you will, or care to admit too. Just because YOU haven't read anything about an RCD causing fire, injury or even a death, doesn't mean it hasn't happened, can't happen, won't or will happen!! Smugness like this, just doesn't become you!!!
What a sorry state the UK TT systems are these day's, ...in the past it was nothing to find many if not most old TT systems with Ra's 5 ohms or lower, even 10 ohms was considered to be on the high side, (even the Yanks talk about trying to improve a 20 ohm Ra with an additional Rod!!) Yet here we are talking in the realms of 200 ohms, and even experienced electricians trying to defend this as all fine and dandy. Why, because we now have the cure-all RCD devices, Oh, ...and it's written in there all seeing all knowing bible, so it must be good-un!! ...lol!!
give up spesh mate...theres plenty of prattle left here yet...lol....Geezus, is this still going. It's getting a bit like War & Peace:tounge_smile:
Geezus, is this still going. It's getting a bit like War & Peace:tounge_smile:
anybody would think you were going to "fill a garden up" with gnomes ...then link em all up in series............whatever happened to depth???......There's far more fiction here than there ever was in War & Peace, I back up my arguments with all available statistics, British Standards and years of experience installing perfectly safe TT installations that meet the requirements of those standards.
Of course, the requirements are guided minima and if anyone wants to fill up a garden with copper to slavishly attempt to attain Ra values akin to a TN system then go for it but at least ponder beforehand the futility and costs of the task!
My boss has had to see to his wife today (who isn`t well)...back in tomorrow....its been boring n all.....Yeah mate, I could sorta tell :lol:. Anyway: Why are'nt you in work today ?
My boss has had to see to his wife today (who isn`t well)...back in tomorrow....its been boring n all.....
anybody would think you were going to "fill a garden up" with gnomes ...then link em all up in series............whatever happened to depth???......
agreed on the depth thing IQ......better to have a higher Ra ...with stability...than a lower one...but only a shallow rod......until the sun pelts down of course..lol...watch it rocket..lol...You'd need some depth to get to TN values in most UK soils!
I'd take a 400 Ohm Ra reading on a 2.4M rod anytime rather than 50 Ohms on a 1M rod though, depth is indeed king!
E54 keeps mentioning this 1M rod as if that's all anyone here uses!
agreed on the depth thing IQ......better to have a higher Ra ...with stability...than a lower one...but only a shallow rod......until the sun pelts down of course..lol...watch it rocket..lol...
so why do we keep seeing these shallow rods ....all connected in series...as if thats gonna do owt..lol.....
There's far more fiction here than there ever was in War & Peace, I back up my arguments with all available statistics, British Standards and years of experience installing perfectly safe TT installations that meet the requirements of those standards.
Of course, the requirements are guided minima and if anyone wants to fill up a garden with copper to slavishly attempt to attain Ra values akin to a TN system then go for it but at least ponder beforehand the futility and costs of the task!
You'd need some depth to get to TN values in most UK soils!
I'd take a 400 Ohm Ra reading on a 2.4M rod anytime rather than 50 Ohms on a 1M rod though, depth is indeed king!
E54 keeps mentioning this 1M rod as if that's all anyone here uses!
i agree that there are other means of earthing (tt) than rods ...such as tape/s and/or plate/s....Rods are available in a few lengths to suit a variety of applications, there could be cases where a rock shelf prevents good depth so multiple rods have to be used, not ideal but it does happen, you are also not just restricted to rods as an electrode...
That's right, would you like to put any money on this one IQ, i've been looking at several well known wholesalers in the UK, and that is the ONLY length they stock, be they 3/8'' or 5/8'' !! I haven't seen one, that stocks 3/4'' rods of any length!!
So that's exactly what everyone is using, unless they are purchasing direct from people like Furse!!!
Do they not also sell a coupler that fits the 1.2M rod giving at X2 the 2.4M that I mentioned a few posts back?
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